Okay, you guys are right on "in-joke," but when I was thinking over the "medium" tag the only alternative I could think of was "genre," which manga obviously is not. I was thinking TV and movies are both on film but are considered different media, so it should be for American comics and manga... but, I don't know, all the definitions are blurry at that level. And format sounds so sterile - it could as easily be paper size or whatever.
I'm still waiting to hear from Support on the tag limits issue, so we'll revisit "char" and make a proper tag discussion post then.